The article describes the course of the colonization of the area between the Alps and the Adriatic from the Early Middle Ages to the modern period. It is divided into four phases. Phase one, i.e., early colonization, covers the period of the spontaneous settling of the Slavic ancestors of present-day Slovenes into the vast area between the Alps and the Adriatic from the second half of the 6th century to the 9th century. This was followed by phase two from the 10th to the end of the 12th century, i.e., systematically organized internal colonization, which mostly involved groups of the excess surrounding population that cleared and drained the plains. Phase three, i.e., systematic, organized hilltop colonization by groups of colonists, lasted until the 15th century, spreading over hilly areas. The colonization continued into the modern period: from the 16th century onward, we speak of phase four, i.e., spontaneous, unplanned, additional colonization by individuals. Throughout the phases, the colonization took place on terrain with different landforms and diverse vegetation. The colonists used various tools to till the land, which influenced the shape of fields and settlements. The new settlers came from near and far, which influenced the structure of the population in the newly colonized area. Under the influence of colonization, both the manor and the peasant‘s position in it changed, while the area originally settled by the ancestors of present-day Slovenes shrank to a third.